Rechargeable Energy Storage Devices (ESD's), such as Lithium Ion Batteries (LiB's) and Super-Capacitors (SC's) are widely used in electronic devices. However, ESD's are generally rigid structures having energy storing active materials of limited thickness and capacity. Moreover, the active materials in LiB cathodes are generally metal oxides that have little or no inherent electrical conductivity. In order to transport electrons throughout the cathode active material, a conductive additive must be employed. Incumbent technology employs some form of carbon black (CB) as the conductive additive, which can limit the usable thickness of the cathode active material layer. Thicker active material layers, in general, require more CB to achieve the needed electrical conductivity. However, if the concentration of CB exceeds about 5% by weight, the material becomes mechanically unstable, and will mud-crack upon drying. This limits the thickness of the cathode layer to less than about 100 microns, requiring many layers to achieve the needed capacity for a full battery. Each layer must have a separator and current collector, which can take up space and add weight without contributing to energy storage capacity. Having thicker active layers would reduce the number of layers in the battery, and therefore the number of separators, thus leading to an increase in volumetric and gravimetric capacity of the overall battery cell.
Well separated, short (<100 microns in length) carbon nanotubes in powder form have been used as conductive additives in LiB cathodes, and have achieved percolation threshold for electron transport in the active material at about 3 times lower concentration than carbon black. However, these powdered CNTs did not impart improvements in mechanical strength.